The bag is made by several layers to insure fireproof. Large bag is enough for bigger batteries velcro-straps are tight and fixed well. Places batteries in Li-Po sack towards the bottom places Li-Po sack on non-flammable surface ensures that charger rate is properly set and polarity is correct for safety. - RC Lipo Lithium Polymer battery safety guard bag - The safest way to store your Lipos - Protect your workshop family and home from the hazard of Lipo charging - This is a fireproof bag designed to stop and contain any fire caused by incorrectly charging or poorly functioning Lipo packs